Interfacial polycarbonate plants currently use a complex system of flakers or prilling units, silos, transfer blowers, and diverter valves to deliver flaked bisphenol A to the reactor. For example, FIG. 1 illustrates post treatment process 10 currently used after the formation of bisphenol A involving the formation of a solid bisphenol A in a flaking unit. FIG. 1 illustrates that crystallized stream 32 is directed to phenol stripping unit 12 to form molten stream 42. Molten stream 42 is then solidified in a flaking unit 14. In flaking unit 14, the molten stream 42 is cooled below the freezing point of bisphenol A and the solidified bisphenol A is then scraped from the flaker drum to form flakes, which then drop into a receiver and are conveyed via flake stream 44 to transfer silos 16 by a blower. From transfer silos 16 the bisphenol A flakes are transferred to storage silos 18, again by a blower. When the bisphenol A is to be used in the polymerization of polycarbonate, the bisphenol A flakes are then transferred from storage silos 18 to polycarbonate production plant 20. In polycarbonate production plant 20, the bisphenol A flakes are weighed in weigh hopper 22 and then the desired amount is added to the reaction vessel.
When producing the bisphenol A flakes or when otherwise handling bisphenol A flakes, a fine bisphenol dust is produced, which consists of high purity bisphenol A. The dust is tacky and difficult to handle and it can be difficult to determine a precise amount of bisphenol A being added to the reaction vessel. Furthermore, handling this dust involves the risk of dust explosions. For this reason, the bisphenol dust is usually disposed of and, for example, incinerated, which entails a costly manual handling procedure and extensive safety precautions due to the risk of dust explosions. The disposal process has the disadvantages that at least a portion of the valuable raw material is being destroying and it has high handling costs. Further still, in order to reduce the risk of explosions in the facility, the bisphenol A flakes need to be stored in a nitrogen environment, requiring the use of nitrogen blanketing in the flaking unit, the transfer silos, and the storage silos and oxygen monitors need to be located at various points in the system to ensure a low oxygen content.
An improved method of transferring bisphenol A stream is therefore desired.